1. Field of the Invention
The present invention generally relates to a biosensor and detection method by using the same, in particular to a multiplex fiber optic biosensor and detection method by using the same.
2. Description of the Related Art
A fiber optic biosensor directs light waves produced by light sources to a to-be-detected region by means of optical fiber, and physical or chemical quantity in the to-be-detected region, such as variations in stress, strain, temperature, refractive index and molecular concentration will cause change of light wave's characteristic, so the variations in the physical or chemical quantity in the to-be-detected region can be obtained by the change of light wave's characteristic. When the sensing signal of a fiber optic sensor is transmitted in optical fiber, there are less electromagnetic noise and magnetic interference, and influence of ionization radiation is evitable through radiation processing, so that it is applicable to tough environment, such as nuclear power plant. Moreover, the same optical fiber can be served as a sensor and signal transduction line, and size of the sensor is usually smaller than traditional one, so that it can be placed in tiny region or zone where is not easy to reach.
A fiber optic sensor excites and transmits signal by means of light without using electric current or voltage, so it is away from danger to electric shock and applicable to medical measurement. The material of optical fiber has characteristics of corrosion resistance so to fit into being used in deep sea engineering as well as chemical corrosion environment, and also with better biological compatibility. Because the temperature tolerance of glass optical fiber is better than that of metal strain gauges, and both the long-term stability and fatigue life of glass optical fiber are better than resistance strain gauge, it is suitable to be used for long-term monitoring works. As optical fiber has been utilizing in long distance communication, the technology related to fiber optic sensor is therefore easy to be conducted for long distance measurements. In addition, the Wavelength-Division Multiplexing in optical communication also contributes to the multipoint measurement in the same optical fiber; consequently, fiber optic sensors have been widely used in fields pertaining to aerospace, medicine, chemistry, geotechnical engineering and civil engineering and so on and so forth.
With reference to FIG. 1 for a schematic diagram of a known fiber optic biosensor. Firstly, when light sources of multiple wavelengths λ1, λ2, λ3 . . . λn are coupled to an optical fiber 100, the lights with different wavelengths are separated by grating, prism, or spectrograph 110, and signals with different wave bands are received by means of Charge Coupled Devices (CCDs), photodiodes, photomultiplier tubes, or an array-based detector. The known fiber optic biosensor, however, has the following disadvantages: when light signals of multiple wavelengths are being separated via grating, prism, or spectrograph 110, the signals cannot be well-resolved if the wavelengths are too close, resulting in inaccuracy of measurement. Furthermore, such a design requires that the quantity of the detection units has to be equal to the quantity of light sources which emit lights with different wavelengths. As a result, the total cost of the detection units will increase if a sample has multiple analytes to be analyzed; besides, it is also inevitable to raise the cost due to the usage of spectrometer.
Recently, the development of nanomaterials becomes more and more important in relevant research and applications, such as photoelectronics, energy, biomedical sensing instrument and so on. The reason for the prosperity lies in that the nanomaterials typically have special characteristics as compared to the bulk materials. One special property of noble metal nanoparticles, which is “the free electron cloud on surface of noble metal nanoparticle is excited by electromagnetic field with specific frequency and further responses in collective dipole resonance, but the vivid electron clouds are localized at the nanoparticle,” is called as Localized Surface Plasmon Resonance (LSPR) or called as Particle Plasmon Resonance (PPR). When the noble metal nanoparticle senses the variation in refractive index of the medium surrounding it, the frequency and intensity of the particle plasmon resonance band will also be changed. By observing the absorption band of noble metal nanoparticle, it can be found that when the refractive index raises, the absorption band of the particle plasmon resonance will move to longer wavelength and the absorbance will be increased; besides, as far as the characteristic of scattering light is concerned, it can be found that when the refractive index raises, the band of the scattering light will also move to longer wavelength and the intensity of light will be increased. Finally, when a specific molecular recognition unit is modified on the nanoparticle surface to have sensing ability of specificity, and by analyzing the relationship between either the frequency or intensity of the resonance band and the concentration of the analyte, the corresponding measurement method is thereby established. The method mainly depends on modifying the noble metal nanoparticles on the optical fiber so as to form a noble metal nanoparticle layer, wherein the noble metal nanoparticle layer is composed of one of spherical noble metal nanoparticle, square noble metal nanoparticle, pyramidal noble metal nanoparticle, rod-shaped noble metal nanoparticle and shell-shaped noble metal nanoparticle, and the noble metal nanoparticles are not connected with each other. The noble metal may be gold, silver or platinum. The absorption variation in evanescent wave of the noble metal nanoparticle plasmon resonance can be accumulated by consecutive multiple total internal reflections along the optical fiber, so as to increase the PPR signal and strengthen the sensing sensitivity. After combining with molecular recognition unit, it is of specificity together with high sensing sensitivity, so that it has a potential of being developed as real time sensing instrument.